As the use of navigation systems increases in both the public and military sectors, there is an incentive to improve their robustness and to decrease the size of their individual components. One such component is the crystal oscillator, which supplies a stable clock frequency derived from the mechanical resonance of a piezoelectric crystal. Crystal oscillators may also be found in products such as test equipment, watches, and electronic circuits. Variants of the crystal oscillator engineered to reduce the impact of environmental factors such as temperature and humidity include the temperature-controlled (or -compensated) crystal oscillator (TCXO), the microcomputer-compensated crystal oscillator (MCXO) and the oven-controlled crystal oscillator (OCXO).
A TCXO, for example, typically includes a control chip electrically connected to the piezoelectric crystal oscillator. Traditionally, the control chip and the crystal are packaged in separate carriers that are then bonded together. The crystal may be attached to its carrier with epoxy, and electrical connections made between the two carriers. For example, the two carriers may be positioned on top of one another and soldered together. In some constructions, one end of the crystal is mounted inside its carrier using two small bumps of conductive epoxy. The two bumps may provide both the support and electrical contacts for the crystal.
Unfortunately, this arrangement may expose the crystal to local stresses at the attachment point that can deleteriously affect its performance and reliability. For example, considerable stress may occur when the package is subjected to an inertial load or a harsh environment. If the elastic limits of the structure (or portions thereof) are exceeded, a permanent change in the TCXO frequency can occur.
Many limitations of these conventional crystal packaging schemes have been addressed by harnessing the crystal oscillator in a flexible membrane, rather than mounting the crystal at discrete points. Installing a bare crystal in the flexible membrane generally involves opening the membrane by inserting some type of pin and/or rod within the membrane's slits. These pins typically remain in place while the crystal is inserted within the flexible membrane. Once the crystal is properly inserted, the pins may be removed by sliding them out, leaving the flexible membrane snugly harnessing the crystal.
Unfortunately, this type of approach tends to be extremely labor intensive and time consuming, and it risks damaging the crystal. The use of pins or other spacers also tends not to provide an accurate or consistent opening of the flexible membrane, and the pins and/or crystal may become dislodged during the process. Further, removal of the pins once the crystal is inserted may result in a shift of the crystal's position within the flexible membrane, and contact between the pins and the crystal may damage the crystal. Specifically, the pins may scratch or chip the surface of the crystal, which may degrade the performance and/or reliability of the crystal (or the device in which it resides).